Dehydration of natural gas streams and cold separation units therefor



Jan. 21, 1958 's. A. WiLSON 5 9 DEHYDRATION OF NATURAL GAS STREAMS ANDcow SEPARATION UNITS THEREFOR Filed Jan. 27, 1955 INVENTOR. 5. A. WilsonATTORNEY 2,826,833 DEHYDRATTQN 61 NATURAL GAS STREAMS AND COLDSEPARATTUN UNTTS THEREFQR damuel A. Vtilson, Minden, La. Application.lanuary 27, 1955, Serial No. 434,454 3 Claims. (ill. 260676) Thisinvention relates to improvements in dehydrating natural gas streams andmore particularly, but not by way of limitation, to a method ofdehydrating natural gas streams in a manner to prevent loss of liquidbath due to control failure, and loss of heat exchange due to depositsof mud or paraffin on the heating coil.

Presently available natural gas stream dehydrating methods have certainoperating difficulties in practical operation. Two of the basic problemsencountered in these systems are loss of the liquid bath utilizedtherein by control failure, and loss of heat exchange through the coilas a result of deposition externally thereon of mud and paraffin usuallypresent in the gas stream.

The present invention contemplates a novel cold separation unitspecifically designed to overcome these detriments. The operation of theunit in general follows the pattern disclosed in United States LettersPatent No. 2,528,028 issued to A. F. Barry on October 31, 1950. Thepresent apparatus, however, comprises a vessel having a horizontalbafile disposed therein to form two compartments for separating thedistillate from the liquid bath for assuring that no paraffin or mudwill come into contact with the heating coil disposed within the bath.it will be apparent that this arrangement will preclude any depositionof paraffin or mud on the heat exchange coil, thereby increasing theefficiency of the apparatus in operation.

It is, therefore, an important object of this invention to provide acold separation unit for removing hydrates from a natural gas streamnormally containing mud and paraflin that will prevent deposition ofthese impurities on the exterior of the heat exchange coil of the unit,thereby increasing the overall efficiency of the operation thereof.

It is another object of this invention to provide a cold separation unitfor removing hydrates from a natural gas stream in a manner to providean efficient control of the liquid bath utilized in the separationprocess in order to prevent loss thereof in operation.

It is still another object of this invention to provide a coldseparation unit for dehydrating a natural gas stream which is simple andefficient in operation and is of an economical construction.

Other objects and advantages of the invention will be evident from thefollowing detailed description, read in conjunction with theaccompanying drawings, which illustrate my invention.

In the drawings:

The figure is a vertical sectional view of a cold separation unitembodying the present invention.

Referring to the drawings in detail, reference char-' acter 1t refersgenerally to a cold separation unit comprising a first stage tank 12 anda second stage tank 14. The second stage tank 14 is preferablysubstantially cylindrical in configuration and is disposed in an uprightvertical position. The tank 14 is provided with a horizontally disposedbaffle 16 for separation thereof into an upper chamber 18 and a lowerchamber 29 for a purpose as will be hereinafter set forth. The lowercompartment 2% is provided with an inlet 22 in communication with alower coil 24. The lower coil 24 connects to and is preferably anintegral part of an upstanding passageway or pipe 26 which extendsupward through the bafile 16 into the upper compartment 13.

States Patent The pipe 26 is in direct communication with an upper heatexchange coil 28 disposed entirely within the upper chamber 18. A liquidbath 19 surrounds the coil 28 for a purpose as will hereinafter be setforth. The upper coil 28 terminates at an outlet 36 which connects witha pipe 32 for communication with the first stage tank 12. The tank 12 issimilar in shape to the tank 14 but is preferably of a smaller size. Asuitable valve 34 connects with a line 36 at the lower portion of thetank 12 to permit discharge of liquid and residue from the tank 12 aswill be hereinafter set forth in detail. Any suitable drain 38 isprovided in the tank 12. The line 36 provides communication between thefirst stage tank 12 and the lower compartment 20 of the second stagetank 14. A drain 40 is disposed at the bottomof the compartment 20 topermit discharge of residue therefrom. An outlet 42 is provided at thetop of the tank 12 for cooperation with a line 44, a choke 45, and aninlet 46 to communicate gases from the tank 12 to the upper chamber 18of the tank 14. An equalizer pipe 43 extends upwardly within the chamber18 and has a lower portion 49 of larger diameter in communication withan upstanding passageway 5% extending downwardly through the partition16 and into the chamher 26 for a purpose as will be hereinafter setforth. An

angled pipe 51 cooperates with an outlet 52 disposed in the upperportion of the chamber 18 for permitting the discharge of gasestherefrom. The chamber 18 may be further provided with a plurality ofsafety outlets 54 if desired.

Operation A natural gas stream containing a mixture of hydrocarbons andwater components in both the vapor and liquid phases initially entersthe inlet 22in the second stage tank 14 from a high pressure distillateoil well (not shown). The gas is usually at a high temperature andpressure as it enters the tank and flows through the coil 24, whereinheat is given up to liquids within the chamber 20 as will be hereinafterset forth. The influent stream travels upward through the passageway 26to enter the coil 28. The temperature of the gas is only slightlyreduced as it passes through the coil. 24. It will, therefore, beapparent that the heat of the gas passing through the heat exchange coil23 will maintain the liquid bath 19 in chamber 18 at a high temperaturefor a purpose as will be hereinafter set forth. The temperature of thegas is greatly reduced by its passage through the heat exchange coil 28,thus substantially reducing the dew point of the gas. The gas passesfrom the coil 28 for discharge at the outlet 3% through, the line 32into the first stage tank 12. Parafiin and mud will not precipitate frominfluent gas at high temperatures. Thus the hot gas stream passingthrough the coil 28 will not permit any accumulation of parafin or mudtherein. As the gas is cooled, however, and enters the tank12, theparaflin and mud will be precipitated With the water in liquid form. Theliquid or distillate will fall by gravity to the bottom of the tank 12as shown at 56. The valve 34 coacting with any suitable liquid levelcontrol means 53 will maintain a desired liquid level within the tank.Suitable baflles 59 may beprovided within the tank 12 for protection'ofthe level con trol means 58 from the pressure of the influent gas streamenteringv the vessel thereabove. Upon opening of the valve 34 thedistillate will be transported into the lower chamber 20 wherein areservoir 60 is maintained, to surround the coil 24. All the parafiinand mud in the. flow. stream will be carried in thisliquidprecipitate Itwill be particularly noted that this liquid precipitate is never incontact with the exterior of the coi128, thereby precluding anypossibility of deposition of paraffin or mud thereon to hinder theoperation of the unit 10. It will also be apparent that the heat givenup by the gas stream passing through the coil 24 as previously mentionedwill prevent freezing of the reservoirliquid 69, particularly in thewinter months to maintain an efficient operation of the apparatus at alltimes. The liquid level within the chamber 20 may be controlled by meansof any suitable level control 62, cooperating with an outlet valve (notshown) similar to the valve 34 in tank 12. I 1

The gases or vapor components remaining within the upper portion of thetank 12 will-flow through the outlet 42 and line 44 to the choke orreducing valve 45 wherein the pressure of the gas is substantiallyreduced. The temperature of the gas will have been greatly reducedduring its travel through the coil 28, and the pressure reductionprocess lowers the temperature an even greater amount. The hydratesremaining in the gas as it is discharged into the chamber 18 will,therefore, condense from the gas and will gravitate into the liquidbafli 19 within the chamber 13. The temperature of the liquid bath ismaintained sufficiently high by the coil 28 as hereinbefore described tomelt the hydrates falling from the gas stream. The liquid bath 19 willcirculate downward around the heat exchange coil 28 and then upwardthrough the annulus 41 between the riser 50 and the lower extension 49of the pipe 48 where it travels downward through the riser 50 fordischarge into the chamber 20.

Substantially dehydrated gas will remain in the upper portion of thechamber 18 after the hydrates have condensed into the liquid bath 19.This gas will be delivered through line 51 and outlet 52 to atransmission :line (not shown) for passage to a storage tank, orthelike. It will be noted that if failure of the liquid control valve 62in the lower chamber 20 occurs, the liquidbath 19 will be maintained andsurround the coil 28 so that the. hydrates falling therein will bemelted and the gas. will be discharged from the outlet 52 in the normalmanner. During this period some gas will flow down the equalizer line 48into the chamber 20, but this is .not critical as a small orifice typechoke nipple (not shown) may be installed downstream of the outlet valve(not shown) within the chamber 20 to limit the gas flow.

From the foregoing, it will be apparent that the present inventionprovides an efficient separation unit for thedehydration of natural gasstreams. The gas stream containing hydrocarbons and water components inthe vapor and liquid phases at high pressure and temperature is passedthrough a second stage separator to transfer heat to the liquid bath,thereby maintaining it at a sufliciently high temperature to melt thecondensed hydrates falling therein. The gas enters the first stageseparator from the heat exchange coil at a reduced temperature whichcauses precipitation of the water components containing any mud andparaffin present in the gas stream. The cooled gas leaves the firststage tank to pass through a pressure reducing choke and is transferredinto the upper portion of the second stage tank. The reduced temperatureand pressure condition of the gas causes condensation of the hydratescontained therein. The hydrates will, therefore, fall into the liquidbath to be melted therein. The temperature of the liquid bath ismaintained sufliciently high to melt the hydrates by heat transfer fromthe coil disposed therein. All the parafiin and mud is removed from thegas stream before it reaches the liquid bath, thereby preventing anydeposition thereof on the heating coil. In this manner, an efiicientheating of the liquid bath is maintained. The quantity of liquid in thebath is adequately controlledto assure an efiicient operation of theseparation unit.

Changes may be made in the combination and arrangement of parts asheretofore set forth in the specification and shownin the drawings,.itbeing understood that any modification in the precise embodiment of theinvention may be made within the scope of the following claims withoutdeparting from the spirit of the invention.

I claim:

1. A method of dehydrating a natural gas stream having impuritiestherein, consisting of passing the stream through a heat exchange coilsurrounded by a liquid bath to transfer heat to the bath and cool thestream, maintainingthe liquid bath within a second stage vessel,discharging the cooled stream into a first stage vessel remote from theliquid bath, removing the impurities from the gas stream forprecipitation and accumulation within the first stage vessel, directingthe removed impurities into the lower portion of the second stagevessel, maintaining the removed impurities out of contact with theliquid bath, withdrawing the remaining vapor components of the gasstream from the first stage vessel, reducing the pressure and furthercooling the vapor components of the gas stream to substantially hydrateforming condition, discharging the further cooled gas stream into theupper portion of the second stage vessel, precipitating thehydrates intothe liquid bath for melting the hydrates, substantially precluding lossof the liquid bath, and withdrawing the dee hydrated gas from the upperportion of the second stage vessel.

2. In a cold separation unit for dehydrating a natural gas streamcomprising a first stage tank and a second stage tank, said second stagetank having a bafHe secured therein providing an upper and a lowerchamber, an inlet means disposed within the lower chamber, a heatexchange coil in the upper chamber surrounded by a liquid bath,communication between the inlet means and the heat exchange coil,communication between the heat exchange coil and the first stage tank,means within the first stage tank to transfer precipitates from the gasstream to the lower chamber of the second stage tank, means to conductgas from the first stage tank into the upper chamber of the second stagetank, means to reduce the pressure of the stream to permit hydrates toprecipitate into the liquid bath, means for precluding loss of theliquid bath, and means in the upper chamber of the second stage tank forwithdrawing the dehydrated gas therefrom.

3. A cold separation unit for dehydrating a natural gas stream normallycontaining water, mud and paraflin and comprlsing a first stage vesseland a second stage vessel, said second stage vessel having asubstantially horizontal bafi'le member secured therein to form anupperand a lower compartment, an inlet disposed in the lowercompartment, communication means between the inletand a heat exchangecoil within the upper compartment, a

liquid bath provided in the upper compartment and completely surroundingthe. coil to receive heat therefrom, communicating means between theheating coil and the first stage vessel for directing the cooled gasstream thereto for precipitation of water, mud and paratfin 'from thestream, means for transferring the precipitate to the lower compartmentof the second stage vessel for storage remote from the heat exchangecoil, means for directing the released gas in the first stage vesselthrough a pressure reducing means and into the upper compartment of thesecond stage vessel where the expanded gas condenses the hydratescontained therein to the liquid bath for.

melting the hydrates, means the loss of the liquid bath, and meansprovided in? the upper chamber of the second stage vessel forwithdrawing the dehydrated gas therefrom.

for substantially precluding OTHER REFERENCES Campbell et al.: PetroleumRefiner, vol. 32,-No. 1 January 1953, pages 138-142.

1. A METHOD OF DEHYDRATING A NATURAL GAS STREAM HAVING IMPURITIESTHEREIN, CONSISTING OF PASSING THE STREAM THROUGH A HEAT EXCHANGE COILSURROUNDED BY A LIQUID BATH TO TRANSFER HEAT TO THE BATH AND COOL THESTREAM, MAINTAINING THE LIQUID BATH WITHIN A SECOND STAGE VESSEL,DISCHARGING THE COOLED STREAM INTO A FIRST STAGE VESSEL REMOTE FROM THELIQUID BATH, REMOVING THE IMPURTIES FROM THE GAS STREAM FORPRECIPITATION AND ACCUMULATION WITHIN THE FIRST STAGE VESSEL, DIRECTINGTHE REMOVED IMPURITIES INTO THE LOWER PORTION OF THE SECOND STAGEVESSEL, MAINTAINING THE REMOVED IMPURITIES OUT OF CONTACT WITH THERLIQUID BATH, WITHDRAWING THE REMAINING VAPOR COMPONENTS OF THE GASSTREAM FROM THE FIRST STAGE VESSEL, REDUCING THE PRESSURE AND FURTHERCOOLING THE VAPOR COMPONENTS OF THE GAS STREAM TO SUBSTANTIALLY HYDRATEFORMING CONDITION, DISCHARGING THE FURTHER COOLED GAS STREAM INTO THEUPPER PORTION OF THE SECOND STAGE VESSEL, PRECIPITATING THE HYDRATESINTO THE LIQUID BATH FOR MELTING THE HYDRATES, SUBSTANTIALLY PRECLUDINGLOSS OF THE LIQUID BATH, AND WITHDRAWING THE DEHYDRATE GAS FROM THEUPPER PORTION OF THE SECOND STAGE VESSEL.
 2. IN A COLD SEPARATION UNITFOR DEHYDRATING A NATURAL GAS STREAM COMPRISING A FRIST STAGE TANK AND ASECOND STAGE TANK, SAID SECOND STAGE TANK HAVING A BAFFLE SECUREDTHEREIN PROVIDING AN UPPER AND A LOWER CHAMBER, AN INLET MEANS DISPOSEDWITHIN THE LOWER CHAMBER, A HEAT EXCHANGE COIL IN THE UPPER CHAMBERSURROUNDED BY A LIQUID BATH, COMMUNICATION BETWEEN THE INLET MEANS ANDTHE HEAT EXCHANGE CHANGE COIL, COMMUNICATION BETWEEN THE HEAT EXCHANGECOIL AND THE FIRST STAGE TANK, MEANS WITHIN THE FIRST STAGE TANK TOTRANSFER PRECIPITATES FROM THE GAS STREAM TO THE LOWER CHAMBER OF THESECOND STAGE TANK, MEANS TO CONDUCT GAS FROM THE FIRST STAGE TANK INTOTHE UPPER CHAMBER OF THE SECOND STAGE TANK, MEANS TO REDUCE THE PRESSUREOF THE STREAM TO PERMIT HYDRATES TO PRECIPITATE INTO THE LIQUID BATH,MEANS FOR PRECLUDING LOSS OF THE LIQUID BATH, AND MEANS IN THE UPPERCHAMBER OF THE SECOND STAGE TANK FOR WITHDRAWING THE DEHYDRATED GASTHEREFROM.